Carbon materials such as graphite and coke are already proposed for use as negative electrode materials for nonaqueous electrolyte secondary cells. Among these materials, graphite exhibits a very low discharge potential in the vicinity of the potential of metallic lithium, affording nonaqueous electrolyte secondary cells of high energy density and is therefore one of the materials widely used. However, the conventional secondary cells wherein graphite is used for the negative electrode have the problem that when the cell is allowed to store for a long period of time, the lithium in the carbon material reacts with the electrolyte, causing self-discharge to result in a lower cell capacity.
To overcome this problem, JP-A No. 36108/1998, for example, proposes a nonaqueous electrolyte secondary cell having incorporated therein a graphite material coated with a carbon material of low crystallinity. The proposed cell nevertheless still has the problem of becoming lower in capacity when left storing.